Rule 24: towing and pushing.

What does COLREGs Rule 24 say?

It sets out the lights and shapes for towing and pushing: towing astern (24(a)), the composite unit (24(b)), pushing ahead or towing alongside (24(c)), the second masthead light (24(d)), the vessel or object towed or pushed (24(e) and (f)), the inconspicuous, partly submerged tow (24(g)), and what to do when the prescribed lights cannot be shown (24(h) and (i)).

Which masthead light do the towing lights replace?

Rule 24(a)(i) and 24(c)(i) both put the two (or three) masthead lights in a vertical line 'instead of the light prescribed in Rule 23(a)(i) or (a)(ii)' — that is, in place of either the forward masthead light or the after one.

Rule 24(d) then requires a vessel towing or pushing under (a) or (c) to comply with Rule 23(a)(ii) as well: a second masthead light abaft of and higher than the forward one, which a vessel of less than 50 metres is not obliged to show but may. Read together with Annex I, section 2(e), that means a towing vessel of 50 metres or more shows her vertical towing lights in one masthead position — forward or aft — and a single masthead light in the other.

Is a towing vessel 'restricted in her ability to manoeuvre'?

Not just by towing. Rule 3(g)(vi) counts a vessel engaged in a towing operation 'such as severely restricts' the towing vessel and her tow in their ability to deviate from their course. Rule 27(c) says such a power-driven vessel shows, in addition to her Rule 24(a) lights or shapes, the lights and shapes of Rule 27(b)(i) and (ii): three all-round lights in a vertical line, red, white, red; by day, a ball, a diamond and a ball.

An ordinary tow is not given that status. Rule 18(a) lists vessels not under command, restricted in their ability to manoeuvre, engaged in fishing and sailing — not vessels towing as such.

What lights does a power-driven vessel show when towing astern?

Under Rule 24(a): two masthead lights in a vertical line — three if the tow is more than 200 metres long; sidelights; a sternlight; and a towing light in a vertical line above the sternlight. Rule 24(d) adds Rule 23(a)(ii): at 50 metres or more she must also show a second masthead light; under 50 metres it is optional.

The towing light is yellow, with the same characteristics as the sternlight (Rule 21(d)): the same 135-degree arc, shining aft. From astern, then, a vessel towing shows yellow over white.

How is the length of the tow measured?

Rule 24(a)(i) measures it 'from the stern of the towing vessel to the after end of the tow' — the towline and everything on it, not the towing vessel herself. The third masthead light and the diamond apply when that length exceeds 200 metres.

What shapes does a tow show by day?

When the length of the tow exceeds 200 metres, a diamond shape where it can best be seen — on the towing vessel (Rule 24(a)(v)) and on the vessel or object being towed (Rule 24(e)(iii)). For an ordinary tow of 200 metres or less, Rule 24 prescribes no shape. A diamond is two cones with a common base (Annex I, section 6).

What lights does the vessel being towed show?

Rule 24(e): sidelights and a sternlight, and a diamond shape when the tow exceeds 200 metres. No masthead light. This covers any vessel or object being towed except the inconspicuous, partly submerged ones in 24(g).

What is a composite unit, and what lights does it show?

A pushing vessel and a vessel being pushed ahead that are 'rigidly connected in a composite unit'. Rule 24(b) says they are regarded as a power-driven vessel and show the Rule 23 lights — one vessel's lights, not towing lights. Rule 35(f) treats them the same way in restricted visibility: they give the power-driven vessel's sound signals.

What lights does a vessel pushing ahead or towing alongside show?

If it is not a composite unit, Rule 24(c): two masthead lights in a vertical line (instead of the forward or after masthead light), sidelights and a sternlight — and, under Rule 24(d), a second masthead light if she is 50 metres or more (optional below that). There is no third masthead light and no towing light in 24(c); the yellow towing light belongs to towing astern under 24(a)(iv).

What do vessels being pushed or towed alongside show?

Rule 24(f) says any number of vessels towed alongside or pushed in a group are to be 'lighted as one vessel'. So a vessel pushed ahead (not a composite unit) carries sidelights at her bow and nothing aft; one towed alongside carries sidelights at her bow and a sternlight as well.

How is an inconspicuous, partly submerged tow lit — Rule 24(g)?

Under 25 metres wide, it shows an all-round white light at each end — though a dracone may leave out the forward one. At 25 metres or wider, it adds an all-round white at each side, at the widest point. Longer than 100 metres, it carries more whites in between, so that no gap exceeds 100 metres. By day it shows a diamond at the after end of the last thing towed, and when the tow exceeds 200 metres a second diamond as far forward as practicable.

Rule 22(d) gives those white all-round lights a minimum range of 3 miles. A dracone is a flexible, sausage-shaped towed container for liquids.

What if the tow cannot show its lights?

Rule 24(h): if a tow genuinely cannot carry its 24(e) or (g) lights or shapes, everything possible must be done to light it — or at the very least to show that it is there.

My yacht is towing a disabled boat. Do I need towing lights?

Under engine your yacht is a power-driven vessel (Rule 3(b)), so Rule 24(a) or (c) would apply — and Rule 24(i) covers this. A vessel 'not normally engaged in towing operations', for which it is impracticable to show the 24(a) or (c) lights, is not required to show them when towing another vessel 'in distress or otherwise in need of assistance'. She must still take all possible measures to show the relationship between the two vessels, as authorised by Rule 36, 'in particular by illuminating the towline'.

Rule 36 allows light signals that cannot be mistaken for any other signal in the rules, or a searchlight directed towards the danger, and says strobe lights are to be avoided. In practice, if you can show proper towing lights, show them: 24(i) relieves you only where that is impracticable. The boat you tow is still covered by 24(e) and (h).

What sound signals do a tow and towing vessel make in fog?

Rule 35(c): a vessel engaged in towing or pushing another vessel sounds one prolonged blast followed by two short, at intervals of not more than two minutes. Rule 35(e): the vessel towed — or, if more than one is towed, the last vessel of the tow — if manned, sounds one prolonged followed by three short, at intervals of not more than two minutes, immediately after the towing vessel's signal when practicable.

How might Rule 24 come up in an MCA oral?

It may come up as a lights picture. Examples of the kind of question to be ready for:

“At night you see three masthead lights in a vertical line and a green sidelight. What is she, and what else do you look for?”

“From astern you see a yellow light above a white light. What is it?”

“How is the length of a tow measured, and why does it matter?”

“What's the difference between the lights for towing astern and for pushing ahead?”

“Your yacht, under engine, has taken a disabled motor boat in tow at night and has no towing lights. What does Rule 24(i) allow, and what must you still do?”

Where do candidates go wrong on Rule 24?

The common slips: measuring the tow from the towing vessel's bow; forgetting that 24(d) brings in Rule 23(a)(ii) — a second masthead light, compulsory at 50 metres or more; giving a pushing vessel a towing light; showing the diamond on a tow of 200 metres or less (except the 24(g) tow, which always has one aft); forgetting that the tow shows a diamond too; and calling every towing vessel restricted in her ability to manoeuvre, when Rule 27(c) applies only to a towing operation that severely restricts the towing vessel and her tow in their ability to deviate from their course.